Power generation

Abstract

Excessive swing of the feedwater in power supply apparatus on the occurrence of a transient is suppressed by injecting an anticipatory compensating signal into the control for the feedwater. Typical overshoot occurs on removal of a large part of the load, the steam flow is reduced so that the conventional control system reduces the flow of feedwater. At the same time there is a reduction of feedwater level in the steam generator because of the collapse of the bubbles under increased steam pressure. By the time the control responds to the drop in level, the apparatus has begun to stabilize so that there is overshoot. The anticipatory signal is derived from the boiling power which is a function of the nuclear power developed, the enthalpy of saturated water and the enthalpy of the feedwater injected into the steam generator. From the boiling power and the increment in steam pressure resulting from the transient are anticipatory increment of feedwater flow is derived. Thus increment is added to the other parameters controlling the feedwater.

What we claim is: 
     
       1. Apparatus for generating power including a nuclear reactor, a turbine to be energized from said reactor, a steam generator, connected to said reactor, for deriving energy therefrom, fluid circulating means, connected to said steam generator and said turbine, said fluid circulating means including a first branch for supplying steam from said steam generator to said turbine to energize said turbine and a second branch for supplying feedwater from said turbine to said steam generator, said feedwater supplied to said steam generator to be converted into steam in said steam generator by the energy supplied to said steam generator by said reactor, valve means in said second branch for controlling the flow of said feedwater to said steam generator, and means, responsive to the magnitude of the boiling power produced by said reactor in said steam generator and to the level of the water in said steam generator, for controlling said valve means in accordance with the demand thereon, and wherein the boiling power, herein BP, is given by the equation:   BP=K.sub.1 ·Q.sub.N -a·(h.sub.s -h.sub.fw)·W.sub.fw     wherein   K 1  =a gain dependent on the requirement of the apparatus   Q N  =nuclear power   a=constant dependent on apparatus   h s  =enthalphy of saturated water   h fw  =enthalphy of feedwater injected into the steam generator   W fw  =rate of flow of feedwater.   
     
     
       2. The apparatus of claim 1 including a first function former for converting Q N  into α·h fw , a second function former for converting the steam pressure, herein P s , into α·h s , a summer for producing the factor α·(h s  -h fw ), a multiplier for deriving from the feedwater flow, W fw , the product α·(h s  -h fw )·W fw  and a summer for producing the difference K 1  ·Q N  -α·(h s  -h fw )·W fw . 
     
     
       3. The apparatus of claim 1 wherein the steam generator has a boiling region and a downcomer, the said apparatus including a function former for converting the boiling power, herein BP, into mass of total fluid in both phases in the steam generator, herein M, means for deriving, from BP, the rate of change of the mass of the fluid in said steam generator, with respect to the steam pressure, herein dM/dP, means for deriving from the steam pressure in said steam generator, herein P s , the change in pressure per unit time herein ΔP, a multiplier for multiplying ΔM/ΔP, by ΔP to derive ΔM, a summer for adding the mass of and total fluid in the steam generator and ΔM to drive M+ΔM, the redistribution of mass between said boiling region and said downcomer of said steam generator, means for deriving the time derivative of M+ΔM, to determine the instantaneous difference between feedwater rate of flow and steam rate of flow, herein ΔW fw , to maintain the nominal water level in said steam generating, a summer for deriving the measured difference between feedwater flow, herein W fw , and steam flow W s , means for the difference ΔW fw  -(W fw  -W s ) as an error in the feedwater flow and means, responsive to said error, for operating, said valve means to compensate for said error. 
     
     
       4. The apparatus of claim 1 including means for deriving, from the boiling power and from the difference between measurements of the feedwater flow and of the steam flow, an error signal for departure of feedwater level from the required level and means, responsive to said error signal, for setting the valve means to compensate for said error signal. 
     
     
       5. The apparatus of claim 4 including a proportional plus integral controller interposed between the valve means and the error signal deriving means. 
     
     
       6. The apparatus of claim 4 including a summer for adding the error signal and a signal measuring the departure of the level of water in the steam generator from a setpoint, the compensating means being responsive to the sum of said error signal and the departure measuring signal. 
     
     
       7. The apparatus of claim 1 wherein the valve means includes a main valve and a by-pass valve, said by-pass valve inducting feedwater at low rate and said main valve conducting feedwater at higher rates, said controlling means for the valve means including means for automatically transferring the conducting of feedwater between said main valve and said by-pass valve in dependence upon the demand in said valve means. 
     
     
       8. Apparatus for generating power including a nuclear reactor, a turbine to be energized from said reactor, a steam generator, connected to said reactor, for deriving energy therefrom, fluid circulating means connected to said steam generator and to said turbine, said fluid-circulating means including a first branch for supplying steam from said steam generator to said turbine to energize said turbine, and a second branch for supplying feedwater from said turbine to said steam generator, said feedwater, supplied to said steam generator, to be converted into steam by the energy supplied to said steam generator by said reactor, valve means in said second branch for controlling the flow of feedwater to said steam generator, and means responsive to the departure of the level of the water in said steam generator from a setpoint and to the difference between (a) the steam flow plus an anticipatory error in the feedwater flow; and   (b) the feedwater flow, for controlling the demand of said valve means, said anticipatory error being derived from the boiling power and the rate of change of pressure, and wherein the boiling power, herein BP, is given by the equation:   BP=K.sub.1 ·Q.sub.N -ac·h.sub.s -h.sub.fs)·W.sub.fw     wherein     K 1  =a gain dependent on the requirement of the apparatus   Q N  =nuclear power   a=constant dependent on apparatus   h s  =enthalphy of saturated water   h fw  =enthalphy of feedwater injected into the steam generator   W fw  =rate of flow of feedwater.   
     
     
       9. The apparatus of claim 8 wherein the valve means includes a main valve and a by-pass valve, the by-pass valve conducting the feedwater at low rates and the main valve conducting the feedwater at higher levels and the demand controlling means for the valve means includes means operable automatically to transfer the conducting of feedwater between said main and by-pass valve independence upon the demand of the valve means. 
     
     
       10. In power supply apparatus including a nuclear reactor a turbine to be driven from said reactor, a steam generator, connected to said reactor, for deriving energy therefrom, said steam generator having a boiling region and a downcomer, and fluid circulating connected to said steam generator and to said turbine, said fluid circulating means including a first branch for supplying steam from said steam generator to said turbine and a second branch for supplying feedwater from said turbine to said steam generator; the method of controlling the flow of feedwater to said second branch including:   (a) determining the feedwater flow;   (b) determining the steam flow;   (c) determining the nuclear power delivered by said reactor;   (d) determining the pressure of the steam;   (e) deriving the boiling power from the determined nuclear power, feedwater flow, and steam pressure, and wherein the boiling power, herein BP, is given by the equation:   BP=K.sub.1 ·Q.sub.N -a·(h.sub.s -h.sub.fw)·W.sub.fw     wherein     K 1  =a gain dependent on the requirement of the apparatus   Q N  =nuclear power   a=constant dependent on apparatus   h s  =enthalpy of saturated water   h fw  =enthalphy of feedwater injected into the steam generator   W fw  =rate of flow of feedwater;   (f) deriving from the steam pressure, the increment in pressure produced by any change in the operation of said apparatus;   (g) deriving from the determined boiling power and increment in pressure at a measure of the mass redistribution between said boiling region and said downcomer resulting from said change in the operation of said apparatus;   (h) determining the difference between said feedwater flow and said steam flow;   (i) determining from said determined mass redistribution an anticipatory measure for the incremental feedwater-flow demand resulting from said change in the operation of said apparatus;   (j) determining the difference between said determined anticipatory incremental feedwater-flow demand and the determined difference between said feedwater flow and said steam flow; and   (k) changing the flow of feedwater so as to compensate for the said difference between the determined anticipatory incremental feedwater flow demand said determined difference between said feedwater flow and said steam flow.   
     
     
       11. The method of claim 10 including: (a) determining the difference between the level of the water in the steam generator and a setpoint;   (b) adding the said difference to the difference between the determined anticipatory incremental feedwater-flow demand and the determined difference between the feedwater flow and the steam flow to derive an error signal; and   (c) changing the flow of feedwater so as to compensate for said error signal.